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The male sex hormone testosterone may help restore sexual pleasure in some post-menopausal women, much as erectile dysfunction drugs have given some men back their sex lives, according to research published today in the New England Journal of Medicine.

In an international study of 814 women who were not using estrogen therapy, those who received 300 milligrams of testosterone a day via a patch on the stomach for a year reported an increase of about one-and-a-half more satisfying sexual episodes a month, when corrected for a placebo effect.

Lead researcher Susan Davis says she conducted the study to determine whether testosterone was a suitable alternative for menopausal women who have stopped taking estrogen therapy because of studies linking it to health risks, including breast cancer.

The study, a two-year double-blind clinical trial of women from Canada, the United States, Australia, the United Kingdom and Sweden who reported enjoying sex only 50 per cent of time, was financed by Procter and Gamble Pharmaceuticals, the makers of a testosterone patch currently available in Europe.

Dr. Davis, a professor of women's health at the Monash University in Melbourne, compared two doses, 300 milligrams and 150 milligrams, to a placebo. The women on the higher dose reported 2.1 more satisfying sexual episodes a month. Those on the 150-milligram dose reported 1.2 more episodes. The placebo group experienced an increase of 0.7 episodes a month.

While Dr. Davis must account for the placebo effect in her findings, she points out that women who opt for the treatment will enjoy the combined effect of the testosterone and the placebo.

"There is a placebo effect in terms of sexual function," she says. "If you're prepared to do something about it, there will be a level of improvement."

One expert who was not involved in the research questioned the basis of Dr. Davis's findings. While testosterone is not approved for use by women in Canada, sexual medicine physician Rosemary Basson is concerned that there are doctors who are prescribing it off-label even for young women.

Although testosterone is generally known as a male sex hormone, it is also produced by women's bodies. Little is known about whether lower-than-normal levels of the hormone might cause sexual dysfunction in women, Dr. Basson said.

She points out that psychological factors may also play a role in sexual satisfaction and is concerned that these might not be properly addressed if a drug is used as the sole treatment.

"It's a very unusual thing to do, to use hormone therapy in a non-physiological way," she says, adding that there are no data on long-term risks.

In her practice, Dr. Basson, a clinical professor in the department of psychiatry at the University of British Columbia, steers women suffering from sexual dysfunction toward cognitive behavioural therapy, sex therapy and mindfulness training.

Dr. Davis agrees that testosterone therapy is not a suitable treatment for all women. Still, she insists that many could benefit from the modest improvements her research produced.

"If a post-menopausal woman is having sex on average five times a month and she only finds that pleasurable twice, and you increase that to four out of five times a month, that's pretty good for that woman," she says. "That's going to impact how she communicates with her partner. It has a ripple effect both within their relationship and with the people around them."

As for side effects, there were none that Dr. Davis considers alarming. While the testosterone appeared to cause some side effects long associated with the hormone, such as unwanted hair growth and acne, the placebo group reported similar effects. Of the women using 300 milligrams of testosterone, 30 per cent reported some hair growth; 23 per cent of the placebo group did, too.

Of the more serious side effects, there were no cardiovascular or pre-diabetes markers, which are a concern especially for younger women who don't ovulate and have higher levels of naturally occurring testosterone.

Dr. Davis says she hopes her work contributes to more discussions between women and their doctors about changes to their libidos. Men have had greater permission to talk about their sexual well-being because they could talk about an actual function, the erection, she says, adding that medication may not be the only answer. She advises talk therapy, too.

"Women should understand that sexual health is a really important part of general health."